The present invention relates to a method for manufacturing a stator and a stator manufactured with the manufacturing method.
Japanese Laid-Open Patent Publication No. 2002-176753 describes a method for manufacturing a stator for an inner-rotor type rotating electrical machine. The stator has an annular stator core. The stator core includes an annular portion and a plurality of teeth extending radially inward from the annular portion. A coil is wound around each tooth. A connection wire extends from one coil to another coil.
The stator core may be divided into a plurality of divisional cores to increase the lamination factor of the coils. The divisional cores are formed by dividing the stator core in the circumferential direction. Each divisional core has a single tooth.
The above publication discloses a first winding method and a second winding method for forming coils. With the first winding method, the plurality of divisional cores are arranged in a single line so that their teeth are parallel to one another. A film insulator extends at a basal end of each tooth between the two sides in the circumferential direction. A gap is formed between adjacent divisional cores so that their film insulators overlap each other. In this state, a wire is wound continuously around the teeth to form a coil on each tooth.
With the second winding method, the divisional cores are arranged so that adjacent divisional cores are connected to each other so that they are pivotal relative to one another. In this state, the plurality of divisional cores are arranged annularly so that their teeth are oriented in an outward direction. In this state, a wire is wound continuously around the teeth to form a coil on each tooth. After the coils are formed, the divisional cores are reversed in a manner that their teeth are oriented in a radially inward direction.
With the first winding method, the gap formed between the adjacent divisional cores is determined by the dimensions of their film insulators in the circumferential direction. In other words, the gap between the adjacent divisional cores is relatively small. As a result, space formed on the two sides of each tooth is greater in this arrangement than in the assembled state of the stator core. However, even with such greater space, teeth or coils adjacent to a tooth around which the wire is to be wound may interfere with the wire winding operation of the tooth.
With the second winding method, greater space is formed on the two sides of each tooth as compared with when the first winding method is used. However, each tooth still has a pair of divisional cores arranged on the two sides of the tooth. Such adjacent teeth or coils may interfere with the wire winding operation of each tooth. In this way, the first winding method and the second winding method both fail to provide sufficient space permitting smooth wire winding operations on the teeth.
With both the first winding method and the second winding method, the plurality of divisional cores are simultaneously moved and arranged annularly after the coils are wound. Thus, the connection wires need to be long enough to permit such movement of the divisional cores. In other words, each connection wire needs to be longer than the circumferential direction distance between two divisional cores that are connected by the connection wire in the assembled state of the stator core. Further, with the first winding method, the gap formed between the adjacent divisional cores further lengthens each connection wire.
The electric resistance of each connection wire increases and the motor efficiency decreases as each connection wire becomes longer. Further, long connection wires require a complicated process for shaping the connection wires after the divisional cores are moved and arranged annularly. Moreover, long connection wires increase the size of the stator in the axial direction.
The connection wires may be eliminated by using a bus bar or a current supply wire to electrically connect the coils to one another. However, the use of a bus bar or a current supply wire increases the number of components and increases the number of processes.